Conventional commercial brushless DC motors use Hall-effect (magnetically operated) sensors. The Hall-effect sensors sense the rotor position and provide a signal to an inverter to commutate to the next phase in sequence when the rotor magnet axis reaches a predetermined position. In this way the motor windings are energized so as to maximize the amount of torque output for the motor at any given speed. However the Hall-effect sensors are structures that limit the motor in a number of different ways.
Hall-effect sensors are typically large compared to solid state circuitry components, and for smaller motors there is a problem in finding enough room to properly mount the sensors. However even assuming that the sensors are already provided in a pre-existing motor, since the maximum operating temperature of the sensors is about 150.degree. C., brushless DC motors utilizing these sensors are not suitable for operating temperatures above F isolation class. Also Hall-effect sensors, due to their complexity, temperature limitation, and other reasons, are responsible for reducing the reliability of brushless DC motors. Further, during manufacture there are difficulties in aligning the sensors, and there are high labor and material costs associated therewith, making AC induction motor users hesitant to switch to high efficiency and high power density brushless DC motors. Also there is a complexity of the connection between the motor and the drive, and sensitivity to wiring orientation, when Hall sensors are utilized.
There have been a number of proposals in the past for making sensorless (that is no Hall-effect sensors) brushless DC motors by using the back emf signal and operating it in a particular way. For example by utilizing conventional chips ML 4410 and ML 4411 developed by Micro Linear, controllers for linear mode brushless DC sensorless motor drives are provided which can operate successfully for motor drives at power levels of those normally required for driving hard discs in personal computers, or where efficiency of the motor is not a consideration. Other proposals include those shown in U.S. Pat. Nos. 5,166,583 and 5,223,772. In U.S. Pat. No. 4,928,043, a phased lock loop is used to phase track the back emf, and in a new motor construction can result in a workable sensorless brushless DC motor.
None of the prior art proposals, however, address the problem of existing motors. That is there are literally tens of thousands of existing brushless DC speed regulating motor drives (e.g. six step) with Hall sensors which are operating in a limited capacity, and/or with less maintainability or reliability which are not cost effective to replace. Also, it is desirable to provide new--in addition to retrofit--construction motors or other electrical rotary machines which have a simple yet versatile construction. That is, it is highly desirable to provide new motors with increased reliability compared to conventional motors, precise velocity regulation, simple installation, and reduced motor cost, size, and weight, as well as quicker response due to reduced rotor inertia.
According to the present invention a method of enhancing DC brushless motors is provided, as well as an improved DC motor or like electrical rotary machine, and circuitry suitable for use in electrical motors. The circuitry can be retrofit into existing motors which utilize Hall-effect sensors, replacing those sensors and thereby achieving the advantages of increased reliability, wider temperature operating range, etc. in a cost effective manner, i.e. without having to replace the entire existing motor drive. New motors constructed according to the present invention also achieve the desired results of increased reliability and temperature range compared to conventional brushless DC motors, have precise velocity regulation, are simple to install, and have reduced motor cost, size, and weight compared to conventional motors, and quicker response time due to reduced rotor inertia.
According to one aspect of the present invention a method of enhancing a brushless DC motor having a plurality of Hall-effect sensors and a frequency-to-voltage conversion circuit is provided. The method comprises the steps of: (a) Deactivating or removing the Hall-effect sensors and the frequency-to-voltage conversion circuit, and (b) connecting a commutation error detector circuit and the DC motor to a voltage controlled oscillator and operatively connecting a solid-state circuit to the voltage controlled oscillator to provide output signals substantially the same as the Hall-effect sensors to thereby functionally replace the Hall-effect sensors. Step (b) may be practiced by operatively connecting a plurality of data (D) flip flops and a NAND gate to the VCO, as by connecting a switch between a VCO and a clock pulse (CP) input of each D flip flop. For example three D flip flops may be used and connected to the VCO through a switch.
It is also desirable according to the invention to achieve a number of other advantageous results for the existing motors. For example there may be the further steps of connecting a direction reverse circuit to the solid state circuit of step (b), connecting a start up circuit (e.g. a rotor alignment circuit) to the solid state circuit, and/or connecting a sampling logic circuit to the solid state circuit to construct sampling logic from the outputs of the solid state circuit so that which phase is a non-energized phase may be determined.
The invention also relates to a brushless sensorless electrical rotary machine, whether new or retrofit, such as a DC motor. The machine comprises: A rotor and a stator and including a plurality of windings driven by a multiphase inverter for selectively energizing the windings in sequence. A voltage controlled oscillator for controlling the frequency of the multiphase inverter, and having an output and an input. And, a solid state indirect rotor position sensoring circuit operatively connected to the voltage controlled oscillator output to provide output signals substantially the same as those of Hall-effect sensors. The solid state indirect rotor position sensoring circuit may comprise a plurality (e.g. three) of D flip flops, each having a CP input; and a NAND gate. Alternatively the sensoring circuit may comprise a plurality of inverters, each connected to an AND gate and to a brushless DC gate drive circuit (as in a ML 4410 or ML 4411 chip). Alternatively the sensoring circuit may comprise a programmable logic chip connected to a brushless DC gate drive circuit (e.g. in an ML 4410 or ML 4411 chip) to realize the same outputs as above mentioned.
A start-up circuit may also be connected to the machine, and include a switch for connecting the VCO output signal to the CP inputs of the D flip flops. A direction reverse circuit may be connected to the solid state indirect rotor positioning circuit, a sampling logic circuit may be connected up to the solid state indirect position sensoring circuit to construct sampling logic from the outputs of the solid state indirect rotor position sensoring circuit so that which phase is a non-energized phase may be determined, and a commutation error detection circuit may be connected to the input of the VCO.
The invention also relates to simple solid state circuitry per se which is particularly suited for use in the construction of brushless sensorless DC electric motors, but may have other applicability as well. The solid state circuit according to the invention comprises, in combination, the following elements: A voltage controlled oscillator having an input, and having an output. A plurality of D flip flops, each having a CP input. And, a NAND gate. The voltage controlled oscillator output is connected to the CP inputs of the D flip flops through a switch. A commutation error detector circuit may be connected to the input of the voltage controlled oscillator.
It is the primary object of the present invention to provide new and/or retrofit sensorless brushless DC motors or like electrical machines, and circuitry for achieving desired advantageous results. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.